摘要
The prediction of central bursting defects in the rod extrusion process through conical dies using the upper bound analysisis investigated. A kinematically admissible velocity field, including the radial and angular velocity components, is proposed. A newcriterion is presented to predict the occurrence of the central bursting defects. Parameter bobt, which represents the risk probability ofcracking, is proposed. It is calculated using the shape of the boundary at the entrance by minimizing the total power dissipationduring the extrusion process. When bobt is equal to or greater than bcr, central bursting occurs. Furthermore, the quantitativerelationships between central bursting defects and process parameters （semi die angle, reduction in area and frictional factor） arestudied. The results show that the central bursting defects are affected primarily by the reduction in area and the friction factor. Thepresented criterion is verified by comparing with the FEM simulation data and the results of the published paper.
采用上限分析法对棒材在圆锥形模具中挤压时的中心开裂缺陷进行预测,提出了一个包括径向速度和角速度分量的运动许可速度场,提出了一个新的预测中心开裂缺陷产生的标准,并提出了一个表示开裂程度的参数b_(obt)。通过最小化挤压过程中总功率耗散,采用入口处的边界形状来计算参数b_(obt)。当b_(obt)≥bcr时发生中心开裂现象。此外,研究了中心开裂缺陷与挤压过程参数(模具半锥角、面积减小率和摩擦因数)的关系。结果表明:棒材的中心开裂缺陷主要受面积减小率和摩擦因数的影响。将本文作者所提出的方法与FEM模拟数据及已有文献数据进行了比较。
